1. Field of the Invention
The present invention relates to a measuring tool. More specifically, the present invention relates to a measuring tool in which a movable member is moved to hold a workpiece, where a dimension or a profile of the workpiece is measured from a displacement of the movable member.
2. Description of Related Art
There are conventionally known measuring tools in which a spindle thereof is moved in the axial direction to hold a workpiece, where a dimension or a profile of the workpiece is measured from the displacement of the spindle. Examples of such measuring tools include a micrometer (refer to, for example, U.S. Pat. No. 4,420,887, FIG. 9, FIG. 10, etc.).
The micrometer includes a U-shaped body frame, an anvil provided on one end of the body frame, a spindle supported on the other end of the body frame, the spindle being advanceable and retreatable relative to the anvil in the axial direction, and a feeding mechanism for feeding the spindle.
The feeding mechanism includes a rack provided on the spindle, a pinion meshed with the rack, an outer roller rotatably provided on the body frame and screwed to the pinion, and a coil spring that connects the outer roller and the pinion.
In such an arrangement, when the outer roller is rotated, the pinion screwed to the outer roller will rotate, and thereby the spindle is moved via the rack. When the workpiece is held by the anvil and the spindle, since the spindle can not be moved further, the pinion can not be rotated either. Herein, if only the outer roller is rotated, the coil spring will be wound. Thus, due to the reaction force of the coil spring applied to spindle, a specific measuring force caused by the reaction force of the coil spring will be applied to the workpiece. Further, the outer roller will abut on the body frame so as to be locked.
With such an arrangement, although the feeding mechanism configured by the rack and the pinion is used, the measurement can be conducted with a specific measuring force. Also, since the outer roller can be locked even when the user leaves his hand off the outer roller, slip of the spindle can be prevented.
Other advantages are that, for example, the thread cutting need not to be conducted at high accuracy compared to that of a typical micrometer (namely, a micrometer in which a male screw is formed on a spindle thereof and a female screw is formed on a body thereof) and the spindle can be moved at a high speed.
However, in the micrometer described in the above document, since the feeding mechanism is configured by the rack and the pinion, there will arise the following problem. Specifically, when performing assembling adjustment during manufacture, since positioning the rack and the pinion (for example, adjustment of a backlash) is difficult to do, the assembling work becomes time-consuming and labor-consuming.
To solve this problem, there is suggested a micrometer in which a feeding mechanism has a feed roller that abuts on the spindle, and the spindle is moved by rotating of the feed roller.
Example of such a feeding mechanism is the one which includes an outer roller rotatably supported to the body frame, a feed roller that can rotate around an axis parallel to the axis of the outer roller to move the spindle, a roller holder that holds the feed roller, a spring that presses the outer periphery of the roller holder so that the feed roller is biased toward a direction in which its outer peripheral face is brought into contact with the spindle, a main gear provided on the outer roller, and a sub-gear provided on the feed roller and meshed with the main gear provided on the outer roller, the sub-gear transmitting the rotation of the outer roller to the feed roller.
The feed roller is disposed between the outer roller and the spindle at a position remote from the anvil relative to the outer roller. The roller holder is provided on the body frame in a manner rotatable around the axis of the outer roller.
In such an arrangement, when the outer roller is rotated, the feed roller will rotate, and thereby the spindle abutting on the feed roller will move in the axial direction.
With such an arrangement, since the work of positioning the rack and the pinion, which causes a problem in feeding mechanism configured by the rack and the pinion as shown in the document, is eliminated, the assembling adjustment during manufacture can be facilitated. Also, since the spindle is moved by rotating the feed roller, the spindle can be moved at high speed.
However, with the feeding mechanism having the aforesaid feed roller, since the spindle is moved by a common feed roller both when forward feed is performed for moving the spindle toward the side of the anvil and when reverse feed is performed for moving the spindle toward the side opposite to the anvil, there will arise the following problems.
The feed roller is pressed by the spring so as to be biased toward the direction in which the feed roller is brought into contact with the spindle, and is supported movably in that direction. Thus, when the outer roller is rotated in a forward direction, since a contact surface of a main gear of the outer roller presses a contact surface of a sub-gear of the feed roller toward a direction away from the spindle, the feed roller will be biased toward that direction.
Thus, even though the spindle can be smoothly moved by a biasing force of the spring when performing the reverse feed, in the case where the forward feed is performed, since a biasing force caused by the rotation of the outer roller in the forward direction is applied to the feed roller in an opposite direction to that of the biasing force of the spring, the feed roller will be moved in the direction away from the spindle, and thereby the spindle can not be smoothly moved.
Since the biasing force for pressing the outer periphery of the feed roller toward the spindle changes depending on whether the spindle is moved in the forward direction or in the reverse direction, good operability can not be achieved.